lecture 9 Flashcards
What is the first factor that contributes to disease emergence?
The agent (pathogen)
- Evolution of pathogenic agents
- Increased virulence of microbes like Influenza A by antigenic variation, and giving rise to new strains with endemic/pandemic properties
- Drug resistance
- Resistance of vectors to pesticides
Zoonoses
2/3 emerging infections from wild/domestic animals
Influenza infection associated with pigs, geese, chickens etc
Deforestation/climate change cause animal displacement (Lassa fever).
Humans populating regions near animal reservoirs/vectors (yellow fever, malaria)
Second factor that contributes to emergence of diseases
The Host
- Human inhabiting new areas
- International travel - global dispersion of diseases
- Mass migration of people into unhygienic human settlements
Name 5 factors contributing to emergence (host)
- Immuno-suppression
- Poverty/social inequality
- Unsafe sexual practices
- Changes in agriculture/food patterns - food borne infections
- Outdoor activity
4 factors that contribute to emergence (environment)
- Economic development and land use (urbanisation, deforestation, encroachment)
- Technology and industry in food processing/handling
- Breakdown of public health - war, unrest, overcrowding
- Deterioration in surveillance systems
What bacterial species are located on South Col of Mount Everest
Staphylococcus and Streptococcus spp.
Dormant but alive as frozen in ice and rocks
Source: human skin/faeces
Deforestation
Forces animals into closer human contact
Possibility for agents to breach species barrier
Climate change
Spread of malaria, Dengue, Leishmaniasis:
- Natural disasters
- Habitat change of disease vectors
- More rainfall
- Higher temperatures
- Changes in bird migration direction
Poverty and poor health infrastructure
Major reservoir and source of continued transmission
Lack of funding:
- Poor prioritization of health funds
- Failure to develop adequate health delivery
Poverty - Malnutrition - Severe infectious disease cycle
Drug Resistance and implications
Caused by:
- incorrect prescriptions
- non-adherence by patients
- Counterfeit drugs
- Anti-infective drugs
- Loss of effectiveness
- Community-acquired e.g TB, pneumococcal
- Hospital acquired e.g. enterococcal, MRSA
Can lead to prolonged hospital admissions, higher death rates, more expensive, higher healthcare costs
Urbanization and population displacement
- Population growth leads to overcrowding, substandard housing, unsafe water, poor sanitation etc
- Uninhibited and reckless industrialisation leads to migration of labour population from rural to urban areas in unhygienic squatter settlements
- Refugees and displaced people can cause diarrhoeal and intestinal parasites
- Changes in ecology and increasing deer populations cause lyme disease (Borrelia burgdorferi)
What are important factors to consider in the causation of a disease?
Causation - Initiation of a condition in an individual not previously affected
Things to consider:
- Critical issues e.g. does or doesn’t it cause the condition
Complications
Framework development
Koch’s Postulates
Determining causative of etiologic agent of infectious disease:
- Find evidence of microbe present
- Isolate microbe and cultivate in a lab
- Inoculate a susceptible healthy subject with isolate and observe disease
- Re-isolate agent from this subject
Bradford-Hill framework
- Strength - Large effects make casual relationship more likely, and strong relationships allow co-variable to be identified
- Consistency - Evidence for same findings in more than one study tested separate things?
- Temporality - exposure must precede outcome
- Biological gradient - Greater exposure leads to greater risk
- Plausibility
- Coherence - Does it hold together in light of similar effects caused by something else
- Experiment - Does removing exposure reduce effect
- Analogy - Are there analogous situations that support relationship? Similar pathogen/chemical
Burden of disease
Worldwide - 1 in 5 deaths are children under 5
Of every 10 deaths:
6 - non-communicable
3 - Communicable, reproductive or nutritional
1 - injury/trauma
Leading causes of death:
- Cancer
- Cardiovascular disease
- Parasitic disease
Explain disease burden
- Burden between different countries
- Factors that influence health status of individuals/populations
- Social/political environment: economics, warfare, immigration, socioeconomic class
- Healthcare - Healthcare access and development
Deaths in children aged under 5 from 1990-2020
90-100 deaths per 1000 down to less than 40 deaths per 1000
Where is the greatest under 5 mortality rates
Africa
Methods to detect and quantify pathogens
Culture
Molecular techniques like PCR, qPCR and whole sample sequencing (eDNA)
Advantages and disadvantages of culture
Advantages:
- CPU/MPN counts
- Phenotypic traits
- Pathogenicity
- Biomass
- Cultured means viable!!!#
Disadvantages:
- Containment labs
- Not representative of diversity/proportionality
- Underestimation of actual numbers
- Bacteria can enter VNBC physiological state
Molecular techniques
- Overcome some limitations of culture
- Allow all or targeted populations to be observed
- Cell based or nucleic acid detection based
- Techniques can be combined for greater understanding and resolution
- Still need resolve live/dead tissue
End point vs real-time PCR advantages and disadvantages
End point:
Advantages:
Cheaper,
increased dynamic range of detection
Disadvantages:
- Inhibition
- Low sensitivity
- Low resolution
- Non-automated
- Short dynamic range
- Size based discrimination
- Not quantitative
- Post-PCR sequencing required for conformation
Real time PCR advanatages and disadvantages
Advantages:
- Increased dynamic range of detection
- Quantitative
Disadvantages:
- Expensive
- Requires considerable optimization
- Inhibition
- Design of template DNA and assay
